1. Field of the Invention
The present invention relates to a video controlled article positioning system and, more particularly, to a system for positioning articles such as beam leaded integrated circuits, beam leaded diodes, etc. During manufacturing processes, the articles must be accurately positioned so that multiprobes, bonding tools, etc. may accurately engage contact leads or other portions of each article. The invention utilizes bidirectional video markers and a system of controlling the positioning speed so as to most efficiently position the articles.
2. Description of the Prior Art
In the past, a wide variety of techniques have been used to position articles with varying degrees of precision. Among the simpler of these techniques are the manual positioning systems utilizing a microscope with cross hairs or similar indicia rigidly fixed in the optics. Suitable positioning mechanisms, such as manually operated wormscrews, are operated to move a stage upon which the article is placed to accurately position the article in alignment with the cross hairs. In operations where small quantities of articles of simple geometry are being handled, these systems are excellent both economically and in performance, but as the articles become more complex in detail or larger quantities are handled, these systems become slow, costly, tedious and questionable in results.
Other prior art techniques utilize photocell or photomultiplier tubes which sense various portions of the article for reflected or transmitted light to control voltages to motors which drive a movable stage. Such systems, while sorting well with large articles or articles having a simple geometry, are not readily adapted to positioning articles which are microscopic in dimension or complex in geometry. Also, varying reflectivity and/or absorbency characteristics of articles cause such systems to operate with less accuracy.
Prior art systems also exist which utilize video signals generated by television cameras for positioning articles. One class of television positioning systems, utilizes a computer to compare various portions of the field with a programmed memory. The field is divided into many subdivisions. The presence or absence of a video signal in each subdivision is compared to the programmed memory to produce signals to position the articles. Such systems are complex and expensive where very accurate positioning is required.
Another class of prior art television positioning systems uses various phase characteristics of the video signal to center an article with respect to the television camera. While such systems are useful, they do not generally produce the accuracy that is necessary for small and complex articles.
One such prior art television positioning system is described in U.S. Pat. No. 3,749,830 issued to F. H. Blitchington on July 31, 1973. This system senses an article or pattern associated with the article to produce a first pulse having a time relationship relative to the horizontal and vertical sync pulses indicating the actual position of the article. A timing circuit controlled by the vertical and horizontal sync pulses generates vertical cross hair pulses and horizontal cross hair pulses to which the first pulse is compared. The article is moved until the first pulse has a predetermined time relationship to the vertical and horizontal cross hair pulses.
An improvement over the Blitchington system is described in U.S. Pat. No. 3,899,634 issued to L. J. Montone et al on Aug. 12, 1975. Vertical and horizontal sync signals from a camera are used to generate boundary markers. An edge of each boundary marker indicates a limit for an edge of the article. A coincidence of a boundary marker signal and the video signal of the article causes the article to be moved until there is no coincidence. A problem with the Montone et al arrangement is that the motor drive circuit used to move the article will always send a signal to the motor having the same voltage level. Consequently, a corrective motor always moves the article at the same speed. Therefore, large corrections require an unsuitably large time length for corrections. When the system speed is increased to overcome this deficiency, however, the motor will overshoot for small corrections.
Therefore, a need remains in the prior art for an article positioning system which may be utilized with articles having microscopic dimensions, is fairly simple in operation, and is capable of self-adjusting for either large or small positioning corrections.